Lots of the long distance guys that have fenders will route the wires under the fender along the rolled edge. Then get a 2 part epoxy and totally encase the entire length of wire in epoxy. It will never come loose causing a potential accident plus it's fully waterproof. On the frame or fork you can get tie wraps that have a built in loop of different wire gauges that will hold the wire in place nicely. Look at online electrical supply houses